Add PyROS paper preprint to Pyomo docs reference list

[shermanjasonaf]

Summary/Motivation:

This PR adds, to the PyROS online documentation, a recommendation for PyROS users to cite the preprint at URL: https://optimization-online.org/2026/06/pyros-the-pyomo-robust-optimization-solver/

AI-Use Disclosure

• AI tools were NOT used during the preparation of this PR

Notes for reviewers (optional):

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.14%. Comparing base (39b315e) to head (fbcaa25).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3992   +/-   ##
=======================================
  Coverage   90.14%   90.14%           
=======================================
  Files         917      917           
  Lines      109101   109101           
=======================================
+ Hits        98348    98349    +1     
+ Misses      10753    10752    -1     

Flag	Coverage Δ
builders	29.09% <ø> (-0.01%)	⬇️
default	86.13% <ø> (?)
expensive	35.07% <ø> (?)
linux	87.67% <ø> (-1.98%)	⬇️
linux_other	87.67% <ø> (ø)
oldsolvers	28.03% <ø> (-0.12%)	⬇️
osx	83.12% <ø> (ø)
win	85.42% <ø> (ø)

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